Good blood sugar numbers depend on when you last ate and whether you have diabetes, but the key benchmark is a fasting level of 99 mg/dL or below. That single number, measured after an overnight fast, is the standard marker of healthy blood sugar for adults without diabetes. Other tests capture a broader picture, and the targets shift if you’re managing diabetes or are older with other health conditions.
Fasting Blood Sugar: The Baseline Number
A fasting blood sugar test measures your glucose after at least eight hours without eating, typically first thing in the morning. For a healthy adult, the result falls into one of three categories:
- Normal: 99 mg/dL or below
- Prediabetes: 100 to 125 mg/dL
- Diabetes: 126 mg/dL or above (confirmed on two separate tests)
If your fasting number consistently lands between 100 and 125, you’re in the prediabetes range. That doesn’t mean you’ll develop diabetes, but it signals that your body is starting to struggle with processing glucose efficiently. Lifestyle changes at this stage, particularly diet and exercise, can often bring numbers back to normal.
Blood Sugar After Eating
Your blood sugar naturally rises after a meal, peaking roughly 60 to 90 minutes after you start eating and then gradually falling. The standard check happens at the two-hour mark. For someone without diabetes, a reading below 140 mg/dL at two hours is normal. Anything from 140 to 199 mg/dL suggests prediabetes, and 200 mg/dL or higher points toward diabetes.
Most people without diabetes never test after meals because routine screening uses fasting tests or A1C. But if you’re monitoring at home because your numbers have been borderline, the two-hour post-meal reading gives you practical feedback on how specific foods affect your blood sugar.
A1C: Your Three-Month Average
While fasting and post-meal tests capture a single moment, the A1C test reflects your average blood sugar over the previous two to three months. It measures the percentage of your red blood cells that have glucose attached to them. The ranges are:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A1C is useful because it isn’t affected by what you ate yesterday or whether you were stressed this morning. It shows the bigger trend. A fasting test might look fine on a good day, but an A1C of 6.0% would reveal that your blood sugar has been running higher than normal overall. That’s why many doctors use both tests together for screening.
Targets If You Have Diabetes
If you’ve been diagnosed with diabetes, the goalposts are different. The targets are wider because tight control increases the risk of blood sugar dropping too low (hypoglycemia), which can be dangerous. The typical targets for adults managing type 1 or type 2 diabetes are:
- Before a meal: 80 to 130 mg/dL
- Two hours after starting a meal: below 180 mg/dL
- A1C: below 7% for most adults
These numbers look looser than the ranges for someone without diabetes, and that’s intentional. A fasting reading of 120 mg/dL would flag prediabetes in a healthy adult, but it’s a perfectly good number for someone on insulin or diabetes medication. The goal is staying in a safe zone that minimizes both high and low episodes over the course of a day.
Continuous Glucose Monitors and Time in Range
If you wear a continuous glucose monitor (CGM), the most important metric isn’t any single reading. It’s the percentage of time your blood sugar stays between 70 and 180 mg/dL, known as “time in range.” An international consensus of diabetes specialists recommends that adults with type 1 or type 2 diabetes aim to spend at least 70% of the day in that range, which works out to roughly 16 hours and 48 minutes. For older adults or those at higher risk of complications, the target drops to 50% or more (about 12 hours).
Time in range is a more complete picture than A1C alone. Two people can have the same A1C but very different daily patterns. One might have steady glucose all day, while the other swings between highs and lows that average out to the same number. The CGM data reveals those swings, which helps with fine-tuning diet, medication timing, and activity.
How Targets Change With Age
For older adults managing diabetes, the priority shifts from hitting tight numbers to avoiding dangerous lows. Hypoglycemia is especially risky in older people because it can cause falls, confusion, and heart problems. As a result, A1C targets are relaxed based on a person’s overall health and independence, not their age alone.
An older adult who is otherwise healthy and active typically aims for an A1C of 7% or below, similar to younger adults. Someone who depends on help with daily activities has a target closer to 8%. For those who are frail or living with dementia, the target rises to 8.5%, and the emphasis is simply on preventing symptoms from blood sugar that’s too high or too low. At every stage, the logic is the same: tighter control carries risks that may outweigh the long-term benefits when life expectancy or daily function is limited.
What Low Blood Sugar Looks Like
Good blood sugar isn’t just about avoiding highs. A reading below 70 mg/dL is considered low (hypoglycemia), and below 54 mg/dL is seriously low. Symptoms include shakiness, sweating, a fast heartbeat, irritability, and difficulty concentrating. If you don’t have diabetes and you’re not on medication that lowers blood sugar, true hypoglycemia is uncommon. But if you’re on insulin or certain diabetes medications, lows are a real and recurring concern.
The practical takeaway: when you’re evaluating whether your numbers are “good,” you’re looking for readings that stay above 70 and below the upper targets for your situation. Consistency matters more than any single reading.
Quick Reference by Test Type
- Fasting (no diabetes): 99 mg/dL or below
- Two hours after eating (no diabetes): below 140 mg/dL
- A1C (no diabetes): below 5.7%
- Fasting (with diabetes): 80 to 130 mg/dL
- Two hours after eating (with diabetes): below 180 mg/dL
- A1C (with diabetes): below 7% for most adults
- CGM time in range (with diabetes): at least 70% of the day between 70 and 180 mg/dL